Help--totally screwed XP MBR

[virusdoc]

I spent the last two weeks playing around with FC2 and convincing myself that I wanted to use it as my primary OS. During this time I had installed it as a single boot on a spare hard drive. However, since I was now convinced this was more than a short-term love affair with Linux, I wanted to set up FC2 on a dual boot with my old XP hard disk.

So I had my old XP system, still intact, on one hard disk (hd0) and I then put in a new blank hd1 to do a fresh install of FC2. When it came time to choose the GRUB configuration, I chose to put GRUB not on the MBR but on the first sector of hd1--which the help text seemed to recommend for a dual boot NT/ FC2 system (I interpreted "NT" to be equivalent to XP).

On reboot: "Error loading operating system". Nothing will load at all. I'm posting this now from the old FC2 install on the spare HD, which thankfully I saved.

I tried everything with the Windows XP Pro CD to repair the XP disk: fixmbr, fixboot, bootcfg /rebuild. The recovery console definitely recognizes the XP session is installed on hd0, but I can't boot to it.

What do I do? If I must, I can reinstall XP completely. But that's 8-12 hrs of my life I'd rather not waste. (Thankfully, I backed up all documents/files to DVD-R prior to this). I know the XP session is intact, the mbr is just hosed in some bizarre fashion. Any help would be most appreciated.

[imdeemvp]

if you are still using fc2 as primary edit your grub.conf ....make sure your xp drive is connected as slave in you pc and follow this instructions to do the edit:

if xp is install in slave drive this is the correct line:

edit your grub.conf, open terminal and type: su and your root pass
[imdeemvp@localhost imdeemvp]$ su
Password:
[root@localhost imdeemvp]# gedit /etc/grub.conf <- this the command to edit the grub

and add this lines to the end:

title Win XP
map (hd0) (hd1)
map (hd1) (hd0)
rootnoverify (hd1,0)
chainloader +1

[Taldor]

I've had the same problem, for me it worked to chang some bios setting of the hard drive to LBA instead of AUTO. (I tried to reinstall windows but even that didn't work.)

[virusdoc]

Thanks--changing to LBA mode got Windows to boot just fine if it was the only disk.

Interestingly, although editing the grub.conf file as imdeemvp suggested does give me a "Windows XP" boot option, it still won't boot into Windows when selected. It just stares at me.

What's up with not being able to use "Auto" as the disk type? Since I'm running on a 120 GB drive, it MUST use LBA, so the Auto BIOS setting should default to that anyway. Does this mean that attempting to install a dual boot FC2 has somehow altered the physical structure of my XP disk?

[Prometheus]

it very well could have. If your XP drive is the primary, Fedora had to put a pointer on that drive that would point to the GRUB installed on your Fedora drive. Thus, it would have changed it. As for LBA, Windows just doesnt like being side-by-side with another os, so LBA basically forces it to co-exist with another os. Without LBA, you would probably get one or the other, never be able to boot the other. Personally, my favorite solution is to use a hardware switch like Nicklock (you can find it a newegg). Use 'em with Maxtor drives, and you can even set up a swap partition that both os's can see (Maxtor drives are slave w/o jumper, which allows this)... but i digress, Auto on the hdd basically just looks for the first one it can find, be it Linux or windows. Lba, breaks up the sequence somehow, and forces it to see both.

[nlawalker]

I was snooping around and happened to find this in the GRUB documentation:

"In traditional disk calls (called CHS mode), there is a geometry translation problem, that is, the BIOS cannot access over 1024 cylinders, so the accessible space is limited to at least 508 MB and to at most 8GB. GRUB can't universally solve this problem, as there is no standard interface used in all machines. However, several newer machines have the new interface, Logical Block Address (LBA) mode. GRUB automatically detects if LBA mode is available and uses it if available. In LBA mode, GRUB can access the entire disk. "

I would imagine that GRUB won't use LBA for some reason unless it is explicitly chosen in the BIOS, as opposed to "Auto." Since it has to do with the range of cylinders that the system can access at this point in the boot process, I'd guess it had to do with where Windows (or Linux) was located on the drive.